There has been nothing much happening for me in the world of moths, or other insects for that matter, with the cold snap extending into February. I’ve run the trap a couple of times since the new year and managed a grand total of one moth: Acleris ferrugana/notana. You can’t tell the two species apart on sight, hence the ambiguous slash between them.
With little to see, and being a bit lazy with birding too because of some busy weekends and cold mornings, I’ve been doing plenty of reading instead, which has meant ‘investing’ in several new books. A new spider field-guide, some generic books on conservation, and this text by Dave Goulson on Bumblebees which I can’t wait to start …
However the first one that turned up was Richard Jones’ new book on the life of Beetles, so the Bumblebees and spiders will have to wait …
It’s a wait that will be worth it though, because this is a fabulous text. I’d been waiting for it since September when I ordered, only to find that there was a delay in publication. Now, having got it and plunged in, I’ve found that it gives a very complete account of the life history and biology of the this massively diverse group. There is wonderful detail about every aspect of beetles you could imagine, but one particular section captured my attention because it relates to Ivy Bees (Colletes hederae). This is a species that was only first recorded in the UK in 2001 but which has spread quickly and has certainly become abundant in Exmouth. In the late Autumn, as the ivy flowered, these bees were all over the place, nesting on the Maer and visible even on ivy in Exmouth town centre. I was really excited to see them, not least because they seemed somehow special having so recently colonised the UK from mainland Europe. This one was feeding amongst many others, on October 1st, just by the entrance to Exmouth Cricket Club:
But back to the beetles. I’m a complete novice at the Coleoptera and so from this point on I’m simply using Jones’ account to tell his own story; one that I found fascinating. It relates to one particular species, Stenoria analis, a beetle that has a special relationship with ivy bees. Indeed, its English name is the ‘ivy bee blister beetle’ and it is parasitic on them. You can see images of the adult beetle on Steven Falk’s brilliant Flickr resource, here.
Before recounting this relationship it’s worth noting that for most beetles it is the adult stage – what we usually call ‘the beetle’, though of course from the beetle’s perspective it’s often just a short part of their life! – which disperses the species. That’s, of course, why most beetles can fly. Flight allows them to move efficiently to new areas to find good locations for laying eggs and having young. Most beetle larvae are fairly immobile, being a ‘grub’ of some sort. Once hatched they eat their through food that is local to them, and through several changes of skin, then pupate and hatch (though there are lots of variations on this theme of course). This inability of the larvae to move far is why it is so important for beetles to lay eggs, or produce young, in the places where the food source is located – dung beetles being a nice example.
S. analis, however, has a different trick up its sleeve. When the eggs hatch the first instar larvae (called triungulins for their three, rather than two, claws on their tarsi) are mobile, allowing them to run up the stalk of the ivy on which they were carefully laid, and to prepare for a hijack. I’ll let Jones take up the story in his own words from here …
For larvae of this beetle, ‘hijack’ is the right word. Clusters of Stenoria triungulins, huddling on the flower or tall stem, actively attract males of their host bee species. The arrival of the male bees, in a manner exactly reminiscent of the pheromone attraction by which they detect newly emerged females, suggests a chemical lure … The male bees attempt to mate with the triungulin cluster, easily allowing the Stenoria larvae to clamber aboard. These are later delivered to female bees during genuine copulation, and end up back in the nests being excavated by these females as they unload pollen masses into the brood cells. The Stenoria larvae then go through similar hypermetamorphosic costume changes [similar to other ‘normal’ beetles]. It seems too easy.
Too easy indeed! Though the process of getting there is spectacularly clever. What’s also clever is that S. analis has found this way to increase its distribution mobility. Not only is the adult beetle able to fly, but the larvae too, by having legs that allow it to crawl and the genetic cunning to lure male ivy bees in, can mobilise the species across wider distributions. Jones predicts that, particularly with this mobility, it won’t be long before it is in the UK … which makes it something exciting to look for.
Still, finding new beetles might not actually be that difficult worldwide. In a wonderful section (pp.326-8) Jones describes the many different estimates for beetle species and the history of attempts to calculate it. Whilst estimates vary wildly, the current best ones come in at between 1 and 3 million (yes, that’s 1 – 3,000,000) different species … the vast majority of which have not yet been identified and named!
I’ll stick to the UK. Still plenty of ID for me to work on, starting with the 102 different families of beetle that Jones lists in his book.